How do I unlink a product to my account?

You cannot remove a product from your Sonos account, it will remain there. This will not do any harm to your account but if you wish get in touch with Sonos support via email see...

https://www.sonos.com/en-us/support/w2c/education

My apologies if I'm misunderstanding the question; as I'm in the USA.🤔

I may be wrong but If you factory reset a speaker it is no longer registered to your account. To my understanding without a factory reset to remove the product from one's account it would be near impossible (if gifted or sold) to be added as a new component for a subsequent owner.

It’s my understanding that even a factory reset doesn’t delete the device from your account, it’s actually the act of someone else registering it to their own account that triggers the change?

As I understood it, the TO is going to return a newly purchased product to the retailer. So I hope the retailer will factory reset the unit.

A factory reset would indeed remove any personal data from the speaker, the way I understand the process. But removing the item from their Sonos account wouldn't happen until it was assigned to someone else's Sonos account, according to what I think I know about that process.

My response was to AjTrek's post. I did not bother to translate the original question, since you had already responded.

A factory reset would indeed remove any personal data from the speaker, the way I understand the process. But removing the item from their Sonos account wouldn't happen until it was assigned to someone else's Sonos account, according to what I think I know about that process.
This is correct, currently there isn't a way to specifically delete one Sonos speaker from your account. You could create a second account under a different email, and register that unit to your second account, which would remove it from the first one... but that might be too much work to just remove a serial number from the profile page.